A semiconductor apparatus for providing a multiplicity of power supply voltages (hereinafter referred to as system power supply IC) has been increasingly used as power supply unit in a system which incorporates large scale integrated circuits (LSIs). For example, a system power supply unit IC 400 as shown in FIG. 4 has a multiplicity of voltage regulating circuits (herein after referred to as power supply circuits) 11–1n for supplying a multiplicity of predetermined output voltages Vo1–Von by stepping up or stepping down the voltage supplied thereto. These output voltages Vo1–Von are supplied to external load circuits (not shown) from the output terminals Po1-Pon of the respective power supply circuits 11–1n. Condensers Co1–Con are provided to smooth the respective outputs.
Each of the multiple power supply circuits 11–1n has a monitoring circuit for monitoring internal voltage, current, and temperature of the power supply circuit. If the monitoring circuit detects an over-voltage, over-current, and over-heating for example, the circuit issues an abnormality detection signal indicating that the associated power supply circuit is in abnormal condition.
The system power supply IC 400 also has a circuit (referred to as system-off circuit) 21 receiving such abnormality detection signal from the respective power supply circuits 11–1n.
Upon receipt of an abnormality detection signal from any one of the multiple power supply circuits 11–1n, the system-off circuit 21 is activated to shut down the entire system power supply IC 400, thereby preventing the multiple power supply circuits 11–1n and the loads connected thereto from being destructed.
This conventional system power supply IC 400 does not tell which of the multiple power supply circuits 11–1n has encountered malfunction or what malfunction has taken place in the circuits and has been protected, since the entire system power supply IC 400 is shut down as a protective measure in the event of such abnormality. Therefore, it is often difficult to find the source of the abnormality or to replicate the abnormal condition after the protective shut down of the system power supply IC 400. As a consequence, it could take a long time to recover the system power supply IC 400 or could destruct the system power supply IC 400 while forcibly testing the IC 400 under impermissible conditions.